In a related question, I ask how to trick fruit trees into flowering later in the spring by prolonging frozen ground conditions.
However, I'm starting to realize that I don't actually understand what triggers plants to flower in the spring in the first place. Possibilities include:
It seems to me that this is a simple enough question. I'm guessing that plants in a certain genus would have a fairly specific genetic program that would stipulate when they should flower. For example:
If root temperature is greater than X (for greater than Y duration), and daylength is greater than Z, then initiate flowering.
I'm not looking for the specific values (example x = 10 degrees C); the values would likely vary by species or even by plant. I'm just wondering what the primary variables are.
Answer
An answer provided by the University of Guelph Plant Sciences Department (they specialize in Malus):
Flowering of Malus and Prunus is driven primarily by air temperature. Provided sufficient winter chilling has accumulated for a given cultivar, tree growth and bud development will advance when air temps are above approx. 5 degrees Celsius. This process is irreversible. Once enough heat units (degree days) are accumulated, the flowers will open.
Flowering is a complex physiological process within the plant, driven by temperature. Photo-period likely does not play a large role in Malus.
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